Your Blue Willow plate looks like it was made around 1930 or so !! Around 1950 instead of just Japan on the back it would have the "Made In" added. It is still popular here in my area. It is transferware and was an inexpensive "everyday" type glassware. My mother used it as did my grandmother. There are slight variations in the patterns depending on who made it. The pattern tells a story but I forget what it was !! Now plates can range in price from $5. to around $30. depending on age and mark. Its easily found here in the south !!